Method and system for wavelength specific thermal irradiation and treatment

ABSTRACT

A system for direct injection of selected thermal-infrared (IR) wavelength radiation or energy into articles for a wide range of processing purposes is provided. These purposes may include heating, raising or maintaining the temperature of articles, or stimulating a target item in a range of different industrial, medical, consumer, or commercial circumstances. The system is especially applicable to operations that require or benefit from the ability to irradiate at specifically selected wavelengths or to pulse or inject the radiation. The system is particularly advantageous when functioning at higher speeds and in a non-contact environment with the target.

BACKGROUND OF THE INVENTION

This invention relates to the direct injection of selectedthermal-infrared (IR) wavelength radiation or energy into targetedentities for a wide range of heating, processing, or treatment purposes.As will be described below, these purposes may include heating, raisingor maintaining the temperature of articles, or stimulating a target itemin a range of different industrial, medical, consumer, or commercialcircumstances. The methods and system described herein are especiallyapplicable to operations that require or benefit from the ability toirradiate at specifically selected wavelengths or to pulse or inject theradiation. The invention is particularly advantageous when the target ismoving at higher speeds and in a non-contact environment with thetarget. The invention provides for an infrared system of selected narrowwavelengths which is highly programmable for a wide range of endapplications. The invention teaches a new and novel type of infraredirradiation system which is comprised of engineered arrays of mostpreferably a new class of narrow wavelength solid-state radiationemitting devices (REDs), one variant of which will be specificallyreferenced later in this document.

More specifically, this invention is directed to a novel and efficientway of injecting an optimal wavelength of infrared radiation into atarget for the purpose of, in some way, affecting the target'stemperature. To cite a small sampling of examples, the “target” for theinfrared injection may be from a wide variety of items ranging fromindividual components in a manufacturing operation, to a region oftreatment on a continuous coil of material, to food in a cookingprocess, or to human patients in a medical treatment environment.

Though the specific embodiment of the invention described hereafter isan example that relates particularly to a plastic bottle preform reheatoperation, the concepts contained within also apply to many other notedscenarios. It also applies to single-stage plastic bottle blowingoperations wherein the injection-molding operation is performedserially, just prior to the blow-molding operation. In this deployment,for example, the methods and apparatus of the subject invention offersimilar advantages over the known art, but would employ differentsensing and controls to deal with the variation in initial temperatureat the entrance to the reheat section of the process.

In general, an ideal infrared heating system optimally raises thetemperature of a target with the least energy consumption. Such a systemmay comprise a device that can directly convert its electrical powerinput to a radiant electromagnetic energy output, with the chosen singleor narrow band wavelengths that are aimed at a target, such that theenergy comprising the irradiation is partially or fully absorbed by thetarget and converted to heat. The more efficiently the electrical inputis converted to radiant electromagnetic output, the more efficiently thesystem can perform. The more efficiently the radiant electromagneticwaves are aimed to expose only the desired areas on the target, the moreefficiently the system will accomplish its work. The radiation emittingdevice chosen for use should have an instant “on” and instant “off”characteristic such that when the target is not being irradiated,neither the input nor the-output energy is wasted. The more efficientlythe exposed target absorbs the radiant electromagnetic energy todirectly convert it to heat, the more efficiently the system canfunction. For an optimal system, care must be taken to properly selectso that the set of system output wavelengths matches the absorptivecharacteristic of the target. These wavelengths likely will be chosendifferently for different targeted applications of the invention to bestsuit the different absorption characteristics of different materials aswell as to suit different desired results.

In contrast, it is well known in the art and industry to use a range ofdifferent types of radiant heating systems for a wide range of processesand treatments. Technologies that have been available previously forsuch purposes produce a relatively broad band spectrum of emittedradiant electromagnetic energy. They may be referred to as infraredheating, treatment, or processing systems whereas, in actual fact, theyoften produce radiant energy well outside the infrared spectrum.

The infrared portion of the spectrum is generally divided into threewavelength classifications. These are generally categorized asnear-infrared, middle-infrared, and long-infrared wavelengths bands.While exact cutoff points are not clearly established for these generalregions, it is generally accepted that the near-infrared region spansthe range between visible light and 1.5 micrometers. The middle-infraredregion spans the range from 1.5 to 5 micrometers. The long-wave-infraredregion is generally thought to be between 5 and 14 micrometers andbeyond.

The radiant infrared sources that have been used in industrial,commercial, and medical, heating treatment or process equipmentpreviously produce a broad band of wavelengths which are rarely limitedto one section of the infrared spectrum. Although their broad bandoutput may peak in a particular range of the infrared spectrum, theytypically have an output tail which extends well into adjacent regions.

As an example, quartz infrared heating lamps, which are well known inthe art and are used for various process heating operations, will oftenproduce a peak output in the 0.8 to 1 micrometer range. Although theoutput may peak between 0.8 and 1 micrometers, these lamps havesubstantial output in a wide continuous set of wavelength bands from theultraviolet (UV) through the visible and out to about 3.5 micrometers inthe middle-infrared. Clearly, although the peak output of a quartz lampis in the near-infrared range, there is substantial output in both thevisible range and in the mid-infrared ranges. It is, therefore, notpossible with the existing broad spectrum infrared sources to beselective as to the preferred wavelength or wavelengths that would bethe most desired for any given heating, processing or treatmentapplication. It is inherently a wide spectrum treatment or process andhas been widely used because there have not been practical alternativesbefore the present invention. The primary temperature rise in manytargets is due to absorption of thermal IR energy at one or more narrowbands of wavelengths. Thus, much of the broadband IR energy output iswasted.

Nonetheless, quartz infrared lights are widely used in industry for boththe discrete components and the continuous material processingindustries. A variety of methodologies would typically be used to helpdirect the emission from the quartz lamps onto the target under processincluding a variety of reflector-types. Regardless of how the energy isfocused onto the target, the quartz lamps are typically energizedcontinuously. This is true whether the target under process is acontinuously produced article or discrete components. The reason forthis is primarily due to the relatively slow thermal response time ofquartz lamps which typically measure on the order of seconds.

An area of specific need for improved energy injection relates to blowmolding operations. More specifically, plastic bottle stretchblow-molding systems thermally condition preforms prior to stretch blowmolding operations. One aspect of this process is known in the art as areheat operation. In a reheat operation, preforms that have been formedby way of an injection molding or compression molding process areallowed to thermally stabilize to room temperature. At a later time, thepreforms are fed into a stretch blow molding system, an early stage ofwhich heats up the preforms to a temperature wherein the thermoplasticpreform material is at a temperature optimized for subsequentblow-molding operations. This condition is met while the preforms arebeing transported through a heating section along the path to the blowmolding section of the machine. In the blow molding section, thepreforms are first mechanically stretched and then blown into vessels orcontainers of larger volume.

Energy consumption costs make up a large percentage of the cost of afinished article that is manufactured using blow molding operations.More specifically, the amount of energy required with the heretoforestate-of-the-art technology to heat up or thermally conditionPolyethylene Terephthalate (PET) preforms from ambient temperature to105° C. in the reheat section of a stretch blow molding machine is quitesubstantial. From all manufacturing efficiently measures, it will beclearly advantageous from both an economic and an environmentalstandpoint to reduce the energy consumption rate associated with theoperation of the thermal conditioning section of stretch blow moldingsystems.

U.S. Pat. No. 5,322,651 describes an improvement in the method forthermally treating thermoplastic preforms. In this patent, theconventional practice of using broadband infrared (IR) radiation heatingfor the thermal treatment of plastic preforms is described. Quoting textfrom this patent, “In comparison with other heating or thermal treatmentmethods such as convection and conduction, and considering the lowthermal conductivity of the material, heating using infrared radiationgives advantageous output and allows increased production rates.”

The particular improvement to the state-of-the-art described in thispatent relates to the manner in which excess energy emitted during IRheating of the preforms is managed. In particular, this patent concernsitself with energy emitted during the heating process that ultimately(through absorption in places other than the preforms, conduction, andthen convection) results in an increase in the air temperature in theoven volume surrounding the transported preforms. Convection heating ofthe preforms caused by hot air flow has proven to result in non-uniformheating of the preforms and, thus, has a deleterious effect on themanufacturing operation. U.S. Pat. No. 5,322,651 describes a method ofcounteracting the effects of the unintended heating of the air flowsurrounding the preforms during IR heating operations.

As might be expected, the transfer of thermal energy from historicalstate-of-the-art IR heating elements and systems to the targetedpreforms is not a completely efficient process. Ideally, 100% of theenergy consumed to thermally condition preforms would end up within thevolume of the preforms in the form of heat energy. Although it was notspecifically mentioned in the above referenced patent, typicalconversion efficiency values (energy into transported preforms/energyconsumed by IR heating elements) in the range between 5% and 10% areclaimed by the current state-of-the-art blow molding machines. Anyimprovement to the method or means associated with the infrared heatingof preforms that improves the conversion efficiency values would be veryadvantageous and represents a substantial reduction in energy costs forthe user of the stretch blow forming machines.

There are many factors that work together to establish the energyconversion efficiency performance of the IR heating elements and systemsused in the current state-of-the-art blow molding machines. As noted,conventional thermoplastic preforms, such as PET preforms, are heated toa temperature of about 105° C. This is typically accomplished instate-of-the-art blow molding machines using commercially availablebroadband quartz infrared lamps. In high-speed/high-production machinesthese often take the form of large banks of very high wattage bulbs. Thecomposite energy draw of all the banks of quartz lamps becomes a hugecurrent draw amounting to many hundreds of kilowatts on the fastestmachines. Two factors associated with these types of IR heating elementsthat have an effect on the overall energy conversion efficiencyperformance of the overall heating system are the color temperature ofthe lamp filament and the optical transmission properties of thefilament bulb.

Another factor that has a significant impact on the overall energyconversion performance of the thermal conditioning subsystems of thecurrent state-of-the-art blow molding machines is the flux control orlensing measures used to direct the IR radiation emitted by the heatingelements into the volume of the preforms being transported through thesystem. In most state-of-the-art blow molding machines, some measures todirect the IR radiant flux emitted by quartz lamps into the volume ofthe preforms are being deployed. In particular, metallized reflectorswork well to reduce the amount of emitted IR radiation that is wasted inthese systems.

Still another factor that has an impact on the energy conversionefficiency performance of the IR heating subsystem is the degree towhich input energy to the typically stationary IR heating elements issynchronized to the movement of the preforms moving through the heatingsystem. More specifically, if a fixed amount of input energy iscontinuously consumed by a stationary IR heating element, even at timeswhen there are no preforms in the immediate vicinity of the heater dueto continuous preform movement through the system, the energy conversionefficiency performance of the systems is obviously not optimized. Inpractice, the slow physical response times of commercial quartz lampsand the relatively fast preform transfer speeds of state-of-the-art blowmolding machines precludes any attempt of successfully modulating thelamp input power to synchronize it with discrete part movement and,thus, achieve an improvement in overall energy conversion efficiencyperformance.

U.S. Pat. Nos. 5,925,710, 6,022,920, and 6,503,586 B1 all describesimilar methods to increase the percentage of energy emitted by IR lampsthat is absorbed by transported preforms used in a blow molding process.All of these patents describe, in varying amounts of detail, the generalpractice in state-of-the-art reheat blow molding machines to use quartzlamps as the IR heating elements. In a reheat blow molding process,preforms that have previously been injection molded and allowed tostabilize to room temperature are reheated to blowing temperatures justprior to blow molding operations. These above reference patents describehow polymers in general, and PET in particular, can be heated moreefficiently by IR absorption than is possible using conduction orconvection means. These patents document in figures the measuredabsorption coefficient of PET as a function of wavelength. Numerousstrong molecular absorption bands occur in PET, primarily in IRwavelength bands above 1.6 micrometer. Quartz lamps are known to emitradiation across a broad spectrum, the exact emission spectrum beingdetermined by the filament temperature as defined by Planck's Law.

As used in existing state-of-the-art blow molding machines, quartz lampsare operated at a filament temperature of around 3000° K. At thistemperature, the lamps have a peak radiant emission at around 0.8micrometer. However, since the emission is a blackbody type emission, asit is known in the art, the quartz filament emits a continuous spectrumof energy from X-ray to very long IR. At 3000° K., the emission risesthrough the visible region, peaks at 0.8 micrometer, and then graduallydecreases as it begins to overlap the regions of significant PETabsorption starting at around 1.6 micrometer.

What is not described in any of these patents is the effect that thequartz bulb has on the emitted spectrum of the lamp. The quartz materialused to fabricate the bulb of commercial quartz lamps has an uppertransmission limit of approximately 3.5 micrometer. Beyond thiswavelength, any energy emitted by the enclosed filament is, for the mostpart, absorbed by the quartz glass sheath that encloses the filament andis therefore not directly available for preform heating.

For the reasons outlined above, in existing state-of-the-art blowmolding machines that use quartz lamps to reheat PET preforms to blowingtemperatures, the range of absorptive heating takes place between 1micrometer and 3.5 micrometer. The group of patents referenced above(U.S. Pat Nos. 5,925,710, 6,022,920, and 6,503,586 B1) all describedifferent method and means for changing the natural absorptionproperties of the preform, thus improving the overall energy conversionefficiency performance of the reheat process. In all of these patents,foreign materials are described as being added to the PET preform stockfor the sole purpose of increasing the absorption coefficient of themixture. These described methods and means are intended to effect thematerials optical absorption properties in the range from the near IRaround 0.8 micrometer out to 3.5 micrometer. While being a viable meansof increasing the overall energy conversion efficiency performance ofthe reheat process, the change in the absorption property of thepreforms that is so beneficial in reducing the manufacturing costs ofthe container also has a deleterious effect on the appearance of thefinished container. A reduction in the optical clarity of the container,sometimes referred to as a hazing of the container, acts to make thisgeneral approach a non-optimal solution to this manufacturing challenge.

U.S. Pat. No. 5,206,039 describes a one-stage injection molding/blowmolding system consisting of an improved means of conditioning andtransporting preforms from the injection stage to the blowing stage ofthe process. In this patent, the independent operation of an injectionmolding machine and a blow molding machine, each adding a significantamount of energy into the process of thermally conditioning thethermoplastic material, is described as wasteful. This patent teachesthat using a single-stage manufacturing process reduces both overallenergy consumption rates and manufacturing costs. This reduction inenergy consumption comes primarily from the fact that most of thethermal energy required to enable the blow molding operation is retainedby the preform following the injection molding stage. More specifically,in a one-stage process as described in the '039 patent, the preform isnot allowed to stabilize to room temperature after the injection moldingprocess. Rather, the preforms move directly from the injection moldingstage to a thermal conditioning section and then on to the blow moldingsection.

The thermal conditioning section described in the '039 patent has theproperties of being able to add smaller amounts of thermal energy aswell as subjecting the preforms to controlled stabilization periods.This differs from the requirements of a thermal conditioning section inthe 2-stage process of a reheat blow-molding machine wherein largeamounts of energy are required to heat the preforms to the blowingtemperature. Though the operation of single-stage injection molding/blowmolding machines are known in the art, finished container qualityproblems persist for these machines. These quality problems are linkedto preform-to-preform temperature variations as the stream of preformsenters the blowing stage. Despite the advances described in the '039patent, using heretofore state-of-the-art IR heating and temperaturesensing means and methods, the process of thermally conditioningpreforms shortly after they have been removed from an injection moldingprocess still results in preforms of varying thermal content enteringthe blowing stage. The variations in thermal content of the enteringpreforms result in finished containers of varying properties andquality. Inefficiencies in the ability to custom tune the IR heatingprocess on a preform-to-preform basis results in manufacturers opting touse a reheat blow molding method to achieve required quality levels. Forthis reason, for the highest production applications, the industry'sreliance on reheat methods persists. Also, because preforms are oftenmanufactured by a commercial converter and sold to an end user who willblow and fill the containers, the re-heat process continues to bepopular.

The prospect of generally improving the efficiency and/or functionalityof the IR heating section of blow molding machines is clearlyadvantageous from both an operating cost as well as product qualityperspective. Though several attempts have been made to renderimprovements in the state-of-the-art IR heating subsystems, cleardeficiencies still persist. Through the introduction of novel IR heatingelements and methods, it is the intention of the present invention toovercome these deficiencies.

In the solid state electronics realm, solid-state emitters or LEDs arewell known in the art. Photon or flux emitters of this type are known tobe commercially available and to operate at various wavelengths from theultraviolet (UV) through the near-infrared. LEDs are constructed out ofsuitably N- and P-doped semiconductor material. A volume ofsemiconductor material suitably processed to contain a P-doped regionplaced in direct contact with an N-doped region of the same material isgiven the generic name of diode. Diodes have many important electricaland photoelectrical properties as is well known in the art. For example,it is well known within the art that, at the physical interface betweenan N-doped region and a P-doped region of a formed semiconductor diode,a characteristic bandgap exists in the material. This bandgap relates tothe difference in energy level of an electron located in the conductionband in the N-region to the energy level of an electron in a loweravailable P-region orbital. When electrons are induced to flow acrossthe PN-junction, electron energy level transitions from N-regionconduction orbitals to lower P-region orbitals begin to happen resultingin the emission of a photon for each such electron transition. The exactenergy level or, alternately, wavelength of the emitted photoncorresponds to the drop in energy of the conducted electron.

In short, LEDs operate as direct current-to-photon emitters. Unlikefilament or other blackbody type emitters, there is no requirement totransfer input energy into the intermediate form of heat prior to beingable to extract an output photon. Because of this directcurrent-to-photon behavior, LEDs have the property of being extremelyfast acting. LEDs have been used in numerous applications requiring thegeneration of extremely high pulse rate UV, visible, and/or near IRlight. One specific application wherein the high pulse rate property ofLEDs has been particularly useful is in automated discrete part visionsensing applications, where the visible or near infrared light is usedto form a lens focused image which is then inspected in a computer.

Unlike filament-based sources, LEDs emit over a relatively limitedwavelength range corresponding to the specific bandgap of thesemiconductor material being used. This property of LEDs has beenparticularly useful in applications wherein wavelength-selectiveoperations such as component illumination, status indication, or opticalcommunication are required. More recently, large clusters of LEDs havebeen used for larger scale forms of visible illumination or even forsignaling lights such as automotive tail lights or traffic signallights.

SUMMARY OF THE INVENTION

The subject invention provides for the implementation of small orsubstantial quantities of infrared radiation devices that are highlywavelength selectable and can facilitate the use of infrared radiationfor whole new classes of applications and techniques that have not beenavailable historically.

An object of this invention is to provide a molding or other process ortreatment system with a thermal IR heating system possessing improved IRenergy conversion efficiency performance.

Another object of this invention is to provide an IR heating systemhaving IR penetration depth performance tuned to the particular materialbeing processed or targeted.

Another object of this invention is to provide a thermal IR radiationsystem which can incorporate an engineered mixture of REDs which produceIR radiation at such selected narrow wavelength bands as may be optimalfor classes of applications.

Another object of this invention is to provide an IR heating systemcapable of being driven in a pulsed mode; said pulsed mode beingparticularly suited to providing IR heat to discretely manufacturedparts as they are transported during the-manufacturing process or tofacilitate synchronous tracking of targets of the irradiation.

Another object of this invention is to provide IR heating elements thatare more directable via metallized reflector elements.

Another object of this invention is to provide an IR heating systemcapable of working in conjunction with a preform temperature measurementsystem to provide preform-specific IR heating capability.

Another object of this invention is to provide IR heating elements thatare fabricated as arrays of direct current-to-photon IR solid-stateemitters or radiance emitting diodes (REDs).

Yet another advantage of this invention is to provide an infraredirradiation system of substantial radiant output at highly specificsingle or multiple narrow wavelength bands.

Yet another advantage of this invention is the functionality to producepowerful, thermal infrared radiation and to be highly programmable forat least one of position, intensity, wavelength, turn-on/turn-off rates,directionality, pulsing frequency, and product tracking.

Yet another advantage of the invention is the facilitation of a moreinput energy efficient methodology for injecting heat energy compared tocurrent broadband sources.

Yet another advantage of the invention in heating bottle preforms is inretaining the ability to heat efficiently without requiring additiveswhich reduce the visible clarity and appearance qualities of thefinished container.

Yet another object of this invention is to provide a general radiantheating system for a wide range of applications to which it can beadapted to provide the increased functionality of wavelength selectiveinfrared radiation in combination with the programmability and pulsingcapability.

Yet another advantage of this invention is the ability to facilitateextremely fast high intensity burst pulses with much higherinstantaneous intensity than steady state intensity.

Yet another advantage of the invention is that waste heat can be easilyconducted away to another location where it is needed or can beconducted out of the using environment to reduce non-target heating.

Yet another advantage of the invention is that the RED devices can bepackaged in high density to yield solid state, thermal IR output powerlevels that have heretofore not been practically attainable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a portion of an exemplarysemiconductor device implemented in one embodiment of the presentinvention.

FIG. 2 is a cross-sectional view of a buffer layer of an exemplarysemiconductor device implemented in one embodiment of the presentinvention.

FIG. 3 is a cross-sectional view of a quantum dot layer of an exemplarysemiconductor device implemented in one embodiment of the presentinvention.

FIG. 4 is a cross-sectional view of a radiation emitting diode includinga quantum dot layer implemented in one embodiment of the presentinvention.

FIG. 5 is a cross-sectional view of a radiation emitting diode includinga quantum dot layer implemented in one embodiment of the presentinvention.

FIG. 6 is a cross-sectional view of a radiation emitting diode includinga quantum dot layer implemented in to one embodiment of the presentinvention.

FIG. 7 is a cross-sectional view of a laser diode including a quantumdot layer implemented in one embodiment of the present invention.

FIG. 8 shows a graphical representation of a single RED semiconductordevice.

FIGS. 9 and 10 show the relative percentage of infrared energytransmitted through a 10 mil thick section of PET as a function ofwavelength.

FIGS. 11 a, 11 b, and 11 c show a typical ensemble of individual REDemitters packaged together into a RED heater element.

FIGS. 12 a and 12 b show the preferred deployment of RED heater elementswithin a blow moliεr.

FIG. 13 shows a preferred method for the thermal treatment of preformsas described by this invention.

FIGS. 14-16 show alternate methods for the thermal treatment ofthermoplastic preforms according to this invention.

FIG. 17 shows RED heater elements being advantageously applied to adynamically transported part.

DETAILED DESCRIPTION OF THE INVENTION

The benefits of providing wavelength specific irradiation can beillustrated by looking at a hypothetical radiant heating example. Assumethat a material which is generally transparent to electromagneticradiation from the visible range through the mid-infrared range requiresprocess heating to support some manufacturing operation. Also assumethat this generally transparent material has a narrow but significantmolecular absorption band positioned between 3.0 and 3.25 micrometers.The example described above is representative of how the presentlydescribed embodiments might be most advantageously applied withinindustry. If the parameters of this particular process heatingapplication dictated the use of radiant heating techniques, the currentstate-of-the-art would call for the use of quartz lamps operated at afilament temperature of approximately 3000° K. At this filamenttemperature, fundamental physical calculations yield the result thatonly approximately 2.1% of the total emitted radiant energy of a quartzlamp falls within the 3.0 to 3.25 micrometer band wherein advantageousenergy absorption will occur. The ability to generate onlywavelength-specific radiant energy output as described within thisdisclosure holds the promise of greatly improving the efficiency ofvarious process heating applications.

The subject invention is directly related to a novel and new approach tobe able to directly output substantial quantities of infrared radiationat selected wavelengths for the purpose of replacing such broadband typedevices.

Recent advances in semiconductor processing technology have resulted inthe availability of direct electron-to-photon solid-state emitters thatoperate in the general mid-infrared range above 1 micrometer (1,000nanometers). These solid state devices operate analogous to common lightemitting diodes (LEDs), only they do not emit visible light but emittrue, thermal IR energy at the longer mid-infrared wavelengths. Theseare an entirely new class of devices which utilize quantum dottechnology that have broken through the barriers which have preventeduseable, cost effective solid state devices from being produced whichcould function as direct electron to photon converters whose output ispseudo-monochromatic and in the mid-infrared wavelength band.

To distinguish this new class of devices from the conventional shorterwavelength devices (LEDs), these devices are more appropriatelydescribed as radiance or radiation emitting diodes (REDs). The deviceshave the property of emitting radiant electromagnetic energy in atightly limited wavelength range. Furthermore, through propersemiconductor processing operations, REDs can be tuned to emit atspecific wavelengths that are most advantageous to a particular radianttreatment application.

In addition, innovations in RED technology related to the formation of adoped planar region in contact with an oppositely doped region formed asa randomly distributed array of small areas of material or quantum dotsfor generating photons in the targeted IR range and potentially beyondhas evolved. This fabrication technique, or others such as thedevelopment of novel semiconductor compounds, adequately applied wouldyield suitable pseudo-monochromatic, solid-state mid-infrared emittersfor the subject invention. Alternate semi-conductor technologies mayalso become available in both the mid-infrared as well as for longwavelength infrared that would be suitable building blocks with which topractice this invention.

Direct electron (or electric current)-to-photon conversions ascontemplated within these described embodiments occur within a narrowwavelength range often referred to as pseudo-monochromatic, consistentwith the intrinsic band-gap and quantum dot geometry of this fabricateddiode emitter. It is anticipated that the half-power bandwidths ofcandidate RED emitters will fall somewhere within the 20-500 nanometerrange. The narrow width of infrared emitters of this type should supporta variety of wavelength-specific irradiation applications as identifiedwithin the content of this complete disclosure. One family of REDdevices and the technology with which to make them are subject of aseparate patent application, U.S. application Ser. No. 60/628,330, filedon Nov. 16, 2004, entitled “Quantum Dot Semiconductor Device” and namingSamar Sinharoy and Dave Wilt as inventors, which application isincorporated herein by reference.

According to this “Quantum Dot Semiconductor Device” application,semiconductor devices are known in the art. They are employed inphotovoltaic cells that convert electromagnetic radiation toelectricity. These devices can also be employed as light emitting diodes(LEDs), which convert electrical energy into electromagnetic radiation(e.g., light). For most semiconductor applications, a desired bandgap(electron volts) or a desired wavelength (microns) is targeted, and thesemiconductor is prepared in a manner such that it can meet that desiredbandgap range or wavelength range.

The ability to achieve a particular wavelength of emission or electronvolt of energy is not trivial. Indeed, the semiconductor is limited bythe selection of particular materials, their energy gap, their latticeconstant, and their inherent emission capabilities. One technique thathas been employed to tailor the semiconductor device is to employ binaryor tertiary compounds. By varying the compositional characteristics ofthe device, technologically useful devices have been engineered.

The design of the semiconductor device can also be manipulated to tailorthe behavior of the device. In one example, quantum dots can be includedwithin the semiconductor device. These dots are believed to quantumconfine carriers and thereby alter the energy of photon emissioncompared to a bulk sample of the same semiconductor. For example, U.S.Pat. No. 6,507,042 teaches semiconductor devices including a quantum dotlayer. Specifically, it teaches quantum dots of indium arsenide (InAs)that are deposited on a layer of indium gallium arsenide(In_(x)Ga_(1-x)As). This patent discloses that the emission wavelengthof the photons associated with the quantum dots can be controlled bycontrolling the amount of lattice mismatching between the quantum dots(i.e., InAs) and the layer onto which the dots are deposited (i.e.,In_(x)Ga_(1-x)As). This patent also discloses the fact that the latticemismatching between an In_(x)Ga_(1-x)As substrate and an InAs quantumdot can be controlled by altering the level of indium within theIn_(x)Ga_(1-x)As substrate. As the amount of indium within theIn_(x)Ga_(1-x)As substrate is increased, the degree of mismatching isdecreased, and the wavelength associated with photon emission isincreased (i.e., the energy gap is decreased). Indeed, this patentdiscloses that an increase in the amount of indium within the substratefrom about 10% to about 20% can increase the wavelength of theassociated photon from about 1.1 μm to about 1.3 μm.

While the technology disclosed in U.S. Pat. No. 6,507,042 may proveuseful in providing devices that can emit or absorb photons having awavelength of about 1.3 μm, the ability to increase the amount of indiumwithin an In_(x)Ga_(1-x)As substrate is limited. In other words, as thelevel of indium is increased above 20%, 30%, or even 40%, the degree ofimperfections or defects within crystal structure become limiting. Thisis especially true where the In_(x)Ga_(1-x)As substrate is deposited ona gallium arsenide (GaAs) substrate or wafer. Accordingly, devices thatemit or absorb photons of longer wavelength (lower energy gap) cannot beachieved by employing the technology disclosed in U.S. Pat. No.6,507,042.

Accordingly, inasmuch as it would be desirable to have semiconductordevices that emit or absorb photons of wavelength longer than 1.3 μm,there remains a need for a semiconductor device of this nature.

In general, a RED provides a semiconductor device comprising anIn_(x)Ga_(1-x)As layer, where x is a molar fraction of from about 0.64to about 0.72 percent by weight indium, and quantum dots located on saidIn_(x)Ga_(1-x)As layer, where the quantum dots comprise InAs orAl_(z)In_(1-z)As, where z is a molar fraction of less than about 5percent by weight aluminum.

The present invention also includes a semiconductor device comprising aquantum dot comprising InAs or Al_(z)In_(1-z)As, where z is a molarfraction of less than about 5 percent by weight aluminum, and a claddinglayer that contacts at least a portion of the quantum dot, where thelattice constant of the quantum dot and said cladding layer aremismatched by at least 1.8% and by less than 2.4%.

The semiconductor devices include a quantum dot layer including indiumarsenide (InAs) or aluminum indium arsenide (Al_(z)In_(1-z)As where z isequal to or less than 0.05) quantum dots on an indium gallium arsenide(In_(x)Ga_(1-x)As) layer, which may be referred to as anIn_(x)Ga_(1-x)As matrix cladding. The lattice constant of the dots andthe In_(x)Ga_(1-x)As matrix layer are mismatched. The lattice mismatchmay be at least 1.8%, in other embodiments at least 1.9%, in otherembodiments at least 2.0%, and in other embodiments at least 2.05%.Advantageously, the mismatch may be less than 3.2, in other embodimentsless than 3.0%, in other embodiments less than 2.5%, and in otherembodiments less than 2.2%. In one or more embodiments, the latticeconstant of the In_(x)Ga_(1-x)As matrix cladding is less than thelattice constant of the dots.

In those embodiments where the dots are located on an In_(x)Ga_(1-x)Ascladding matrix, the molar concentration of indium (i.e., x) within thiscladding matrix layer may be from about 0.55 to about 0.80, optionallyfrom about 0.65 to about 0.75, optionally from about 0.66 to about 0.72,and optionally from about 0.67 to about 0.70.

In one or more embodiments, the In_(x)Ga_(1-x)As cladding matrix islocated on an indium phosphorous arsenide (InP_(1-y)As_(y)) layer thatis lattice matched to the In_(x)Ga_(1-x)As cladding matrix. In one ormore embodiments, the InP_(1-y)As_(y) layer onto which theIn_(x)Ga_(1-x)As cladding is deposited is a one of a plurality of graded(continuous or discrete) InP_(1-y)As_(y) layers that exist between theIn_(x)Ga_(1-x)As cladding and the substrate onto which the semiconductoris supported. In one or more embodiments, the substrate comprises anindium phosphide (InP) wafer. The semiconductor may also include one ormore other layers, such as In_(x)Ga_(1-x)As layers, positioned betweenthe In_(x)Ga_(1-x)As cladding and the substrate.

One embodiment is shown in FIG. 1. FIG. 1, as well as the other figures,are schematic representations and are not drawn to scale with respect tothe thickness of each layer or component, or with respect to therelative thickness or dimension between each layer comparatively.

Device 1000 includes substrate 1020, optional conduction layer 1025,buffer structure 1030, cladding layer 1040, and dot layer 1050. As thoseskilled in the art appreciate, some semiconductor devices operate byconverting electrical current to electromagnetic radiation orelectromagnetic radiation to electrical current. The ability to controlelectromagnetic radiation or electrical current within these devices isknown in the art. This disclosure does not necessarily alter theseconventional designs, many of which are known in the art ofmanufacturing or designing semiconductor devices.

In one embodiment, substrate 1020 comprises indium phosphide (InP). Thethickness of InP substrate 1020 may be greater than 250 microns, inother embodiments greater than 300 microns, and in other embodimentsgreater than 350 microns. Advantageously, the thickness may be less than700 microns, in other embodiments less than 600 microns, and in otherembodiments less than 500 microns.

In one or more embodiments, the semiconductor devices envisioned mayoptionally include an epitaxially grown layer of indium phosphide (InP).The thickness of this epitaxially grown indium phosphide layer may befrom about 10 nm to about 1 micron.

In one embodiment, optional conduction layer 1025 comprises indiumgallium arsenide (In_(x)Ga_(1-x)As). The molar concentration of indium(i.e., x) within this layer may be from about 0.51 to about 0.55,optionally from about 0.52 to about 0.54, and optionally from about 0.53to about 0.535. In one or more embodiments, conduction layer 1025 islattice matched to the InP substrate.

Conduction layer 1025 may be doped to a given value and of anappropriate thickness in order to provide sufficient electricalconductivity for a given device. In one or more embodiments, thethickness may be from about 0.05 micron to about 2 microns, optionallyfrom about 0.1 micron to about 1 micron.

In one or more embodiments, buffer layer 1030 comprises indiumphosphorous arsenide (InP_(1-y)As_(y)). In certain embodiments, thebuffer layer 1030 comprises at least two, optionally at least three,optionally at least four, and optionally at least five InP_(1-y)As_(y)layers, with the lattice constant of each layer increasing as the layersare positioned further from substrate 1020. For example, and as depictedin FIG. 2, buffer structure 1030 includes first buffer layer 1032,second buffer layer 1034, and third buffer layer 1036. The bottom layersurface 1031 of buffer structure 1030 is adjacent to substrate 1020, andthe top planer surface 1039 of buffer structure 1030 is adjacent tobarrier layer 1040. The lattice constant of second layer 1034 is greaterthan first layer 1032, and the lattice constant of third layer 1036 isgreater than second layer 1034.

As those skilled in the art will appreciate, the lattice constant of theindividual layers of buffer structure 1030 can be increased by alteringthe composition of the successive layers. In one or more embodiments,the concentration of arsenic in the InP_(1-y)As_(y) buffer layers isincreased in each successive layer. For example, first buffer layer 1032may include about 0.10 to about 0.18 molar fraction arsenic (i.e., y),second buffer layer 1034 may include about 0.22 to about 0.34 molarfraction arsenic, and third buffer layer 1036 may include about 0.34 toabout 0.40 molar fraction arsenic.

In one or more embodiments, the increase in arsenic between adjacentbuffer layers (e.g., between layer 1032 and layer 1034) is less than0.17 molar fraction. It is believed that any defects formed betweensuccessive buffer layers, which may result due to the change in latticeconstant resulting from the increase in the arsenic content, will not bedeleterious to the semiconductor. Techniques for using criticalcomposition grading in this fashion are known as described in U.S. Pat.No. 6,482,672, which is incorporated herein by reference.

In one or more embodiments, the thickness of first buffer layer 1032 maybe from about 0.3 to about 1 micron. In one or more embodiments, the topbuffer layer is generally thicker to ensure complete relaxation of thelattice structure.

In one or more embodiments, the individual buffer layer at or near thetop 1039 of buffer structure 1030 (e.g., buffer layer 1036) isengineered to have a lattice constant that is from about 5.869 Å toabout 5.960 Å, optionally from about 5.870 Å to about 5.932 Å.

In one or more embodiments, the individual buffer layer at or near thebottom 1031 of buffer structure 1030 (e.g., buffer layer 1032) ispreferably engineered within the confines of the critical compositiongrading technique. In other words, inasmuch as a first buffer layer(e.g., buffer layer 1032) is deposited on and an InP wafer, the amountof arsenic present within the first buffer layer (e.g., layer 1032) isless than 17 mole fraction.

Cladding layer 1040 comprises In_(x)Ga_(1-x)As. In one or moreembodiments, this layer is preferably lattice matched to the in-planelattice constant of the top buffer layer at or near the top 1039 ofbuffer structure 1030. The term lattice matched refers to successivelayers that are characterized by a lattice constant that are within 500parts per million (i.e., 0.005%) of one another.

In one or more embodiments, cladding layer 1040 may have a thicknessthat is from about 10 angstroms to about 5 microns, optionally fromabout 50 nm to about 1 micron, and optionally from about 100 nm to about0.5 microns.

In one or more embodiments, quantum dot layer 1050 comprises indiumarsenide (InAs). Layer 1050 preferably includes wetting layer 1051 andquantum dots 1052. The thickness of wetting layer 1051 may be one or twomono layers. In one embodiment, the thickness of dots 1052, measuredfrom the bottom 1053 of layer 1050 and the peak of the dot 1055 may befrom about 10 nm to about 200 nm, optionally from about 20 nm to about100 nm, and optionally from about 30 nm to about 150 nm. Also, in oneembodiment, the average diameter of dots 1052 may be greater than 10 nm,optionally greater than 40 nm, and optionally greater than 70 nm.

In one or more embodiments, quantum layer 1050 includes multiple layersof dots. For example, as shown in FIG. 3, quantum dot 1050 may includefirst dot layer 1052, second dot layer 1054, third dot layer 1056, andfourth dot layer 1058. Each layer comprises indium arsenide InAs, andincludes wetting layers 1053, 1055,1057, and 1059, respectively. Eachdot layer likewise includes dots 1055. The characteristics of the eachdot layer, including the wetting layer and the dots, are substantiallysimilar although they need not be identical.

Disposed between each of dot layers 1052, 1054, 1056, and 1058, areintermediate cladding layers 1062,1064, 1066, and 1068, respectively.These intermediate cladding layers comprise In_(x)Ga_(1-x)As. In one ormore embodiments, the In_(x)Ga_(1-x)As intermediate cladding layers aresubstantially similar or identical to cladding layer 1040. In otherwords, the intermediate cladding layers are preferably lattice matchedto barrier layer 1040, which is preferably lattice matched to top bufferlayer 1036. In one or more embodiments, the thickness of intermediatelayers 1062, 1064, 1066, and 1068 may be from about 3 nm to about 50 nm,optionally from about 5 nm to about 30 nm, and optionally from about 10nm to about 20 nm.

As noted above, the various layers surrounding the quantum dot layer maybe positively or negatively doped to manipulate current flow. Techniquesfor manipulating current flow within semiconductor devices is know inthe art as described, for example, in U.S. Pat. Nos. 6,573,527,6,482,672, and 6,507,042, which are incorporated herein by reference.For example, in one or more embodiments, regions or layers can be doped“p-type” by employing zinc, carbon, cadmium, beryllium, or magnesium. Onthe other hand, regions or layers can be doped “n-type” by employingsilicon, sulfur, tellurium, selenium, germanium, or tin.

The semiconductor devices envisioned can be prepared by employingtechniques that are known in the art. For example, in one or moreembodiments, the various semiconductor layers can be prepared byemploying organo-metallic vapor phase epitaxy (OMVPE). In one or moreembodiments, the dot layer is prepared by employing a self-formingtechnique such as the Stranski-Krastanov mode (S-K mode). This techniqueis described in U.S. Pat. No. 6,507,042, which is incorporated herein byreference.

One embodiment of a radiation emitting diode (RED) including a quantumdot layer is shown in FIG. 4. RED 1100 includes base contact 1105,infrared reflector 1110, semi-insulating semiconductor substrate 1115,n-type lateral conduction layer (LCL) 1120, n-type buffer layer 1125,cladding layer 1130, quantum dot layer 1135, cladding layer 1140, p-typelayer 1145, p-type layer 1150, and emitter contact 1155. Base contact1105, infrared reflector 1110, semi-insulating semiconductor substrate1115, n-type lateral conduction layer (LCL) 1120, n-type buffer layer1125, cladding layer 1130, quantum dot layer 1135, and cladding layer1140 are analogous to those semiconductor layers described above.

Base contact 1105 may include numerous highly conductive materials.Exemplary materials include gold, gold-zinc alloys (especially whenadjacent to p-regions), gold-germanium alloy, or gold-nickel alloys, orchromium-gold (especially when adjacent to n-regions). The thickness ofbase contact 1105 may be from about 0.5 to about 2.0 microns. A thinlayer of titanium or chromium may be used to increase the adhesionbetween the gold and the dielectric material.

Infrared reflector 1110 comprises a reflective material and optionally adielectric material. For example, a silicon oxide can be employed as thedielectric material and gold can be deposited thereon as an infraredreflective material. The thickness of reflector 1110 may be form about0.5 to about 2 microns.

Substrate 1115 comprises InP. The thickness of substrate 1115 may befrom about 300 to about 600 microns.

Lateral conduction layer 1120 comprises In_(x)Ga_(1-x)As that is latticematched (i.e. within 500 ppm) to InP substrate 1115. Also, in one ormore embodiments, layer 1120 is n-doped. The preferred dopant issilicon, and the preferred degree of doping concentration may be fromabout 1 to about 3 E19/cm³. The thickness of lateral conduction layer1120 may be from about 0.5 to about 2.0 microns.

Buffer layer 1125 comprises three graded layers of InP_(1-y)As_(y) in afashion consistent with that described above. Layer 1125 is preferablyn-doped. The preferred dopant is silicon, and the doping density may befrom about 0.1 to about 3 E19/cm³.

Cladding layer 1130 comprises In_(x)Ga_(1-x)As that is lattice matchedto the in-plane lattice constant (i.e. within 500 ppm) of the top ofbuffer layer 1125 (i.e. the third grade or sub-layer thereof). In one ormore embodiments, In_(x)Ga_(1-x)As cladding layer 1130 comprises fromabout 0.60 to about 0.70 percent mole fraction indium. The thickness ofcladding layer 1130 is about 0.1 to about 2 microns.

Quantum dot layer 1135 comprises InAs dots as described above withrespect to the teachings of this invention. As with previousembodiments, the intermediate layers between each dot layer includeIn_(x)Ga_(1-x)As cladding similar to cladding layer 1130 (i.e., latticematched). In one or more embodiments, the amount of indium in one ormore successive intermediate cladding layers may include less indiumthan cladding layer 1130 or a previous or lower intermediate layer.

Cladding layer 1140 comprises In_(x)Ga_(1-x)As that is lattice matched(i.e. within 500 ppm) to the top of buffer later 1125 (i.e. the thirdgrade or sub-layer thereof).

Confinement layer 1145 comprises InP_(1-y)As_(y) that is lattice matchedto In_(x)Ga_(1-x)As layer 1140. Also, in one or more embodiments, layer1145 is p-doped. The preferred dopant is zinc and the dopingconcentration may be from about 0.1 to about 4 E19/cm³. The thickness ofconfinement layer 1145 may be from about 20 nm to about 200 nm.

Contact layer 1150 comprises In_(x)Ga_(1-x)As that is lattice matched toconfinement layer 1145. Contact layer 1150 is preferably p-doped (e.g.,doped with zinc.). The doping concentration may be from about 1 to about4 E19/cm³. The thickness of contact layer 1150 is from about 0.5 toabout 2 microns. The contact layer 1150 may be removed from the entiresurface except under layer 1155.

Emitter contact 1155 may include any highly conductive material. In oneor more embodiments, the conductive material includes a gold/zinc alloy.

Another embodiment is shown in FIG. 5. Semiconductor device 1200 isconfigured as a radiation emitting diode with a tunnel junction withinthe p region. This design advantageously provides for lower resistancecontacts and lower resistance current distribution. Many aspects ofsemiconductor 1200 are analogous to semiconductor 1100 shown in FIG. 4.For example, contact 1205 may be analogous to contact 1105, reflector1210 may be analogous to reflector 1110, substrate 1215 may be analogousto substrate 1115, lateral conduction layer 1220 may be analogous toconduction layer 1120, buffer layer 1225 may be analogous to bufferlayer 1125, cladding layer 1230 may be analogous to cladding layer 1130,dot layer 1235 may be analogous to dot layer 1135, cladding layer 1240may be analogous to cladding layer 1140, and confinement layer 1245 maybe analogous to confinement layer 1145.

Tunnel junction layer 1247 comprises In_(x)Ga_(1-x)As that is latticematched to confinement layer 1245. The thickness of tunnel junctionlayer 1247 is about 20 to about 50 nm. Tunnel junction layer 1247 ispreferably p-doped (e.g., with zinc), and the doping concentration maybe from about 1 to about 4 E19/cm³. Tunnel junction layer 1250 comprisesIn_(x)Ga_(1-x)As that is lattice matched to tunnel junction 1247. Thethickness of tunnel junction layer 1250 is from about 20 to about 5,000nm. Tunnel junction layer 1250 is preferably n-doped (e.g., silicon),and the doping concentration is from about 1 to about 4 E19/cm³.

Emitter contact 1255 may include a variety of conductive materials, butpreferably comprises those materials that are preferred for n-regionssuch as chromium-gold, gold-germanium alloys, or gold-nickel alloys.

Another embodiment of an RED is shown in FIG. 6. Semiconductor device1300 is configured as a radiation emitting diode in a similar fashion tothe RED shown in FIG. 5 except that electromagnetic radiation can beemitted through the substrate of the semiconductor device due at leastin part to the absence of the base reflector (e.g., the absence of areflector such as 1210 shown in FIG. 5). Also, the semiconductor device1300 shown in FIG. 6 includes an emitter contact/infrared reflector1355, which is a “full contact” covering the entire surface (orsubstantially all of the surface) of the device.

In all other respects, device 1300 is similar to device 1200. Forexample, contact 1305 may be analogous to contact 1205, substrate 1315may be analogous to substrate 1215, lateral conduction layer 1320 may beanalogous to conduction layer 1220, buffer layer 1325 may be analogousto buffer layer 1225, cladding layer 1330 may be analogous to claddinglayer 1230, dot layer 1335 may be analogous to dot layer 1235, claddinglayer 1340 may be analogous to cladding layer 1240, and confinementlayer 1345 may be analogous to confinement layer 1245, tunnel junctionlayer 1347 is analogous to tunnel junction layer 1247, tunnel junctionlayer 1350 is analogous to tunnel junction layer 1250.

The semiconductor technology envisioned may also be employed in themanufacture of laser diodes. An exemplary laser is shown in FIG. 7.Laser 1600 includes contact 1605, which can comprise any conductivematerial such as gold-chromium alloys. The thickness of contact layer1605 is from about 0.5 microns to about 2.0 microns.

Substrate 1610 comprises indium phosphide that is preferably n-doped ata concentration of about 5 to about 10 E18/cm³. The thickness ofsubstrate 1610 is from about 250 to about 600 microns.

Optional epitaxial indium phosphide layer 1615 is preferably n-doped ata concentration of about 0.2 4 E19/cm³ to about 1 E19/cm³. The thicknessof epitaxial layer 615 is from about 10 nm to about 500 nm.

Grated InP_(1-y)As_(y) layer 1620 is analogous to the gratedInP_(1-y)As_(y) buffer shown in FIG. 2. Buffer 1620 is preferablyn-doped at a concentration at about 1 to about 9 E18/cm³.

Layer 1625 and 1630 form wave guide 1627. Layer 1625 comprises indiumgallium arsenide phosphide (In_(1-x)GA_(x)As_(z)P_(1-z)). Layer 1630likewise comprises In_(1-x)GA_(x)As_(z)P_(1-z). Both layers 1625 and1630 are lattice matched to the top of layer 1620. In other words,layers 1625 and 1630 comprise about 0 to about 0.3 molar fractiongallium and 0 to about 0.8 molar fraction arsenic. Layer 1625 is about0.5 to about 2 microns thick, and is n-doped at a concentration of about1-9 E18/cm³. Layer 1630 is about 500 to about 1,500 nm, and is n-dopedat a concentration of about 0.5 to 1 E18/cm³.

Confinement layer 1635, dot layer 1640, and confinement layer 1645 aresimilar to the dot and confinement layers described above with respectto the other embodiments. For example, confinement layer 1635 isanalogous to confinement layer 1040 and dot layer 1640 us analogous todot layer 1050 shown in FIG. 3. In one or more embodiments, the numberof dot layers employed within the dot region of the laser device is inexcess of 5 dot layers, optionally in excess of 7 dot layers, andoptionally in excess of 9 dot layers (e.g., cycles). Confinement layers1635 and 1645 may have a thickness from about 125 to about 500 nm andare lattice matched to the wave guide. Layers 1635, 1640, and 1645 arepreferably non-doped (i.e., they are intrinsic).

Layers 1650 and 1655 form wave guide 1653. In a similar fashion tolayers 1625 and 1630, layers 1650 and 1655 compriseIn_(1-x)GA_(x)As_(z)P_(1-z) that is lattice matched to the top of buffer1620. Layer 1650 is about 500 to about 1,500 nm p-doped at aconcentration of about 0.5 to about 1 E18/cm³. Layer 655 is about 1 toabout 2 microns thick and is p-doped at a concentration of about 1 toabout 9 E18/cm³.

In one embodiment, layer 1660 is a buffer layer that is analogous tobuffer layer 1620. That is, the molar fraction of arsenic decreases aseach grade is further from the quantum dots. Layer 1660 is preferablyp-doped at a concentration of 1-9 E18/cm³.

Layer 1665 comprises indium phosphide (InP). The thickness of layer 1665is about 200 to about 500 nm thick and is preferably p-doped at aconcentration of about 1 to about 4 E19/cm³.

Layer 1670 is a contact layer analogous to other contact layersdescribed in previous embodiments.

In other embodiments, layers 1660,1665, and 1670 can be analogous toother configurations described with respect to other embodiments. Forexample, these layers can be analogous to layers 1145,1150, and 1155shown in FIG. 4. Alternatively, layers analogous to 1245, 1247,1250, and1255 shown in FIG. 5 can be substituted for layers 1660,1665, and 1670.

Various modifications and alterations that do not depart from the scopeand spirit of these device embodiments will become apparent to thoseskilled in the art.

Of course, it should be appreciated that, in one form, the inventionherein incorporates RED elements as described. However, it should beunderstood that various other device technologies may be employed. Forexample, experimental mid-IR LEDs operating in a range from 1.6micrometers to 5.0 micrometers are known but are not commercialrealities. In addition, various semiconductor lasers and laser diodesmay be employed with suitable modifications. Of course, other enablingtechnologies may be developed for efficiently producing limitedbandwidth irradiation in advantageous wavelengths.

In order to practice the invention for a particular application, it willusually require deploying many suitable devices in order to haveadequate amplitude of irradiation. Again, in one form, these deviceswill be RED devices. In most heat applications of the invention, suchdevices will typically be deployed in some sort of high density x by yarray or in multiple x by y arrays, some of which may take the form of acustomized arrangement of individual RED devices. The arrays can rangefrom single devices to more typically hundreds, thousands, or unlimitednumber arrays of devices depending on the types and sizes of devicesused, the output required, and the wavelengths needed for a particularimplementation of the invention. The RED devices will usually be mountedon circuit boards which have at least a heat dissipation capability, ifnot special heat removal accommodations. Often the RED devices will bemounted on such circuit boards in a very high density/close proximitydeployment. It is possible to take advantage of recent innovations indie mounting and circuit board construction to maximize density wheredesirable for high-powered applications. For example, such techniques asused with flip chips are advantageous for such purposes. Although theefficiency of the RED devices is good for this unique class of diodedevice, the majority of the electrical energy input is converteddirectly into localized heat. This waste heat must be conducted awayfrom the semi-conductor junction to prevent overheating and burning outthe individual devices. For the highest density arrays, they may likelyuse flip-chip and chip-on-board packaging technology with active and/orpassive cooling. Multiple circuit boards will often be used forpracticality and positioning flexibility. The x by y arrays may alsocomprise a mix of RED devices which represent at least two differentselected wavelengths of infrared radiation in a range from, for example,1 micrometer to 5 micrometers.

For most applications, the RED devices will be deployed advantageouslyin variously sized arrays, some of which may be three dimensional ornon-planar in nature for better irradiation of certain types of targets.This is true for at least the following reasons:

-   -   1. To provide sufficient output power by combining the output of        the multiple devices.    -   2. To provide for enough ‘spread’ of output over a larger        surface than a single device could properly irradiate.    -   3. To provide the functionality that the programmability of an        array of RED devices can bring to an application.    -   4. To allow mixing into the array devices that are tuned to        different specified wavelengths for many functional reasons        described in this document.    -   5. To facilitate matching the ‘geometry’ of the output to the        particular application requirement.    -   6. To facilitate matching the devices mounting location,        radiating angles and economics to the application requirements.    -   7. To facilitate the synchronization of the output to a moving        target or for other ‘output motion’.    -   8. To accommodate driving groups of devices with common control        circuitry.    -   9. To accommodate multi-stage heating techniques.

Because of the typical end uses of diodes, they have been manufacturedin a manner that minimizes cost by reducing the size of the junction. Ittherefore requires less semiconductor wafer area which is directlycorrelated to cost. The end use of RED devices will often requiresubstantial radiated energy output in the form of more photons. It hasbeen theorized that REDs could be manufactured with creative ways offorming a large photon producing footprint junction area. By so doing,it would be possible to produce RED devices capable of sustainingdramatically higher mid-infrared, radiant output. If such devices areavailable, then the absolute number of RED devices needed to practicethis invention could be reduced. It would not necessarily be desirableor practical, however, given the high power outputs associated with themany applications of this invention, that the number of devices would bereduced to a single device. The invention can be practiced with a singledevice for lower powered applications, single wavelength applications,or, if the RED devices can be manufactured with sufficient outputcapability.

Similarly, it is possible to manufacture the RED device arrays asintegrated circuits. In such an implementation the REDs would be arrayedwithin the confines of a single piece of silicon or other suitablesubstrate but with multiple junctions that function as the photonconversion irradiation sites on the chip. They could be similar to otherintegrated circuit packages which use ball grid arrays for electricalconnectivity. Such device packages could then be used as the array,facilitating the desired electrical connectivity for connection to andcontrol by the control system. Again, a design parameter is the controlof the junction temperature which should not be allowed to reachapproximately 100° to 105° C., with current chemistries, before damagebegins to occur. It is anticipated that future chemistry compounds mayhave increased heat tolerance but heat must always be kept below thecritical damage range of the device employed. They could further bedeployed either on circuit boards individually or in multiples or theycould be arrayed as a higher level array of devices as dictated by theapplication and the economics.

In designing the best configuration for deploying RED devices intoirradiation arrays, regardless of the form factor of the devices, thedesigner must consider the whole range of variables. Some of thevariables to be considered in view of the targeted application includepackaging, ease of deployment, costs, electronic connectivity, controlto programmability considerations, cooling, environment of deployment,power routing, power supply, string voltage, string geometry,irradiation requirements, safety and many others that one skilled in theappropriate arts will understand.

All raw materials used to manufacture products have associated with themparticular absorption and transmission characteristics at variouswavelengths within the electromagnetic spectrum. Each material also hascharacteristic infrared reflection and emission properties but we willnot spend any time discussing these because the practicing of thisinvention is more driven by the absorption/transmission properties. Thepercent of absorption at any given wavelength can be measured andcharted for any specific material. It can then be shown graphically overa wide range of wavelengths as will be explained and exampled in moredetail later in this document. Because each type of material hascharacteristic absorption or transmission properties at differentwavelengths, for best thermal process optimization it is very valuableto know these material properties. It should be recognized that if acertain material is highly transmissive in a certain range ofwavelengths then it would be very inefficient to try to heat thatmaterial in that wavelength range. Conversely, if the material is tooabsorptive at a certain wavelength, then the application of radiantheating will result in surface heating of the material. For materialsthat are inefficient heat conductors, this is not usually an optimum wayto heat evenly through the material.

The fact that various materials have specific absorption or transmissioncharacteristics at various wavelengths has been well known in the artfor many years. Because, however, high-powered infrared sources were notavailable that could be specified at particular wavelengths, orcombinations of wavelengths, it has not historically been possible tofully optimize many of the existing heating or processing operations.Since it was not practical to deliver specific wavelengths of infraredradiation to a product, many manufacturers are not aware of thewavelengths at which their particular product is most desirously heatedor processed.

This is illustrated this with an example in the plastics industry.Referring to FIGS. 9 and 10, by examining the transmission curve ofPolyethylene terephthalate (PET resin material, as it is known in theindustry), out of which plastic beverage containers are stretch blowmolded, it can be observed that the PET material is highly absorptive inthe long wavelength region and is highly transmissive in the visible andnear-infrared wavelength regions. Its transmission varies dramaticallybetween 1 micrometers and 5 micrometers. Its transmission not onlyvaries dramatically in that range but it varies frequently and abruptlyand often very substantially sometimes within 0.1 micrometers.

For example, at 2.9 micrometers PET has a very strong absorption. Thismeans that if infrared radiation was introduced to PET at 2.9micrometers, it would nearly all be absorbed right at the surface orouter skin of the material. If it were desirable to heat only the outersurface of the material, then this wavelength could be used. Since PETis a very poor conductor of heat (has a low coefficient of thermalconductivity) and since it is more desirable in stretch blow moldingoperations to heat the PET material deeply from within and evenly allthe way through its volume, this is, in practice, a bad wavelength atwhich to heat PET properly.

Looking at another condition, at 1.0 micrometer (1000 nanometers) PETmaterial is highly transmissive. This means that a high percentage ofthe radiation at this wavelength that impacts the surface of the PET,will be transmitted through the PET and will exit without imparting anypreferential heating, hence be largely wasted. It is important to notethat the transmission of electromagnetic energy decreases exponentiallyas a function of thickness for all dielectric materials, so the materialthickness has a substantial impact on the choice for the optimalwavelength for a given material.

It should be understood that while PET thermoplastic material has beenused here as an example, the principles hold true for a very wide rangeof different types of materials used in different industries and fordifferent types of processes. As a very different example, a glue oradhesive lamination system is illustrative. In this example, supposethat the parent material that is to be glued is very transmissive at achosen infrared wavelength. The heat-cured glue that is to be employedmight be very absorptive at that same wavelength. By irradiating theglue/laminate sandwich at this specific advantageous wavelength, theprocess is further optimized because the glue, and not the adjacentparent material, is heated. By selectively choosing these wavelengthinterplays, optimum points are found within various widely diverse kindsof processing or heating applications within industry.

Historically, the ability to produce relatively high infrared radiationdensities at specific wavelengths has simply not been available toindustry. Therefore, since this type of heating or processingoptimization has not been available, it has not been contemplated bymost manufacturers. It is anticipated that the availability of suchwavelength specific infrared radiant power will open entirely newmethodologies and processes. The subject invention will make such newprocesses practical and will provide an implementation technology thathas far reaching flexibility for a wide range of applications. While itis anticipated that the first utilizations of the subject invention willbe in industry, it is also recognized that there will be manyapplications in commercial, medical, consumer, and other areas as well.

It is anticipated that the invention will be very useful as analternative to broadband quartz infrared heating bulbs, or otherconventional heating devices, that are currently in wide usage. Suchquartz bulbs are used for a range of things including heating sheets ofplastic material in preparation for thermo-forming operations. Not onlycan the subject invention be utilized as an alternative to the existingfunctionality of quartz infrared lamps or other conventional heatingdevices, but it can be envisaged to add substantial additionalfunctionality.

The present invention, by contrast, can either generate radiant energyin a continuously energized or alternately a pulsed mode. Because thebasic REDs devices of the subject invention have an extremely fastresponse time which measures in microseconds, it can be more energyefficient to turn the energy on when it is needed or when a targetcomponent is within the targeted area and then turn it off when thecomponent is no longer in the targeted area.

The added functionality of being able to pulse energize the infraredsource can lead to a considerable improvement in overall energyefficiency of many radiant heating applications. For example, bysuitably modulating the energized time of either individual or arrays ofthe infrared radiation emitting devices (REDs), it is possible to trackindividual targets as they move past the large infrared array source. Inother words, the infrared emitting devices that are nearest the targetdevice would be the ones that would be energized. As the targetcomponent or region moves onward, the “energizing wave” could be passeddown the array.

In the case of heating material which will be thermoformed, it could bedesirable to apply more heat input into areas which will get moreseverely formed as compared to areas which will be more modestly formedor not formed at all. It is possible, by correctly designing theconfiguration of infrared emitter arrays, to not only not have all thedevices energized simultaneously but it is possible to energize themvery strategically to correspond to the shape of the area to be heated.For continuously moving production lines, for example, it might be mostdesirable to program a specially shaped area of desired heat profilethat can be programmably moved in synchronous motion with the targetregion to be heated. Consider a picture frame shaped area requiringheating as shown in FIG. 17. In this case, it would be possible to havea similar picture frame shaped array of devices (402) at desired radiantintensity that would programmably move down the array, synchronized withthe movement of the target thermoforming sheet (401). By using anencoder to track the movement of a product such as the (401)thermoforming sheet, well known electronics synchronization techniquescan be used to turn on the right devices at the desired intensityaccording to a programmable controller or computer's instructions. Thedevices within the arrays could be turned on by the control system fortheir desired output intensity in either a “continuous” mode or a“pulsed” mode. Either mode could modulate the intensity as a function oftime to the most desirable output condition. This control can be ofgroups of devices or down to individual RED devices. For a particularapplication, there may not be a need, to have granular control down tothe individual RED devices. In these instances the RED devices can bewired in strings of most desired geometry. These strings or groups ofstrings may then be programmably controlled as the applicationrequirements dictate. Practicality will sometimes dictate that the REDdevices are driven in groups or strings to facilitate voltages that aremost convenient and to reduce the cost of individual device control.

The strings or arrays of REDs may be controlled by simply supplyingcurrent in an open loop configuration or more sophisticated control maybe employed. The fact intensive evaluation of any specific applicationwill dictate the amount and level of infrared radiant control that isappropriate. To the extent that complex or precise control is dictated,the control circuitry could continuously monitor and modulate the inputcurrent, voltage, or the specific output. The monitoring for mostdesirable radiant output or result could be implemented by directlymeasuring the output of the infrared array or, alternatively, someparameter associated with the target object of the infrared radiation.This could be performed by a continuum of different technologies fromincorporating simple thermocouples or pyrometers up to much moresophisticated technologies that could take the form of, for example,infrared cameras. One skilled in the art will be able to recommend aparticular closed loop monitoring technique that is economicallysensible and justifiable for a particular application of the invention.

Both direct and indirect methods of monitoring can be incorporated. Forexample, if a particular material is being heated for the purpose ofreaching a formable temperature range, it may be desirable to measurethe force needed to form the material and use that data as at least aportion of the feedback for modulation of the infrared radiation arrays.Many other direct or indirect feedback means are possible to facilitateoptimization and control of the output of the subject invention.

It should be clearly understood that the shapes, intensities, andenergizing time of the present invention radiant heat source, asdescribed herein, is highly programmable and lends itself to a very highlevel of programmable customization. Often in industry, custom shapes orconfigurations of heat sources are designed and built for a specificcomponent to direct the heating to the correct locations on thecomponent. With the flexible programmability of the subject invention itis possible for a single programmable heating panel to serve as aflexible replacement to an almost infinite number of custom-builtpanels. Industry is replete with a wide variety of infrared ovens andprocessing systems. Such ovens are used for curing paints, coatings,slurries of various sorts and types, and many other purposes. They alsocan be used in a wide variety of different lamination lines for heatfusing materials together or for curing glues, adhesives, surfacetreatments, coatings, or various layers that might be added ⁺o thelamination ‘sandwich’.

Other ovens may be used for a wide variety of drying applications. Forexample, in the two-piece beverage can industry it is common to spray acoating into the interior of the beverage can and then transport themcontinuously by conveyor “in mass” through a long curing oven. Theuncured interior coating has the appearance of white paint uponapplication but after curing becomes nearly clear. In these variousdrying and curing applications with the current invention, it would bepossible to choose a wavelength or combination of wavelengths that arethe most readily and appropriately absorbed by the material that needsto be dried, treated, or cured. In some applications the wavelengthsthat are not present may be more important to an improved process thanthe ones that are present. The undesirable wavelengths may adverselyaffect the materials by drying, heating, changing grain structure ormany other deleterious results which in a more optimum process could beavoided with the subject invention.

Often it is desirable to raise the temperature of a target material tobe cured or dried without substantially affecting the substrate orparent material. It may well be that the parent material can be damagedby such processing. It is more desirable to not induce heat into itwhile still inducing heat into the target material. The subjectinvention facilitates this type of selective heating.

To review another application area for the invention, the medicalindustry has been experimenting with a wide range of visible light andnear-infrared radiant treatments. It has been theorized that certainwavelengths of electromagnetic energy stimulate and promote healing. Ithas also been postulated that irradiation with certain wavelengths canstimulate the production of enzymes, hormones, antibodies, and otherchemicals within the body as well as to stimulate activity in sluggishorgans. It is beyond the scope of this patent to examine any of thespecific details or treatment methodologies or the merit of suchpostulations. The subject invention however, can provide a solid state,wavelength selectable, and programmable mid-infrared radiation sourcethat can facilitate a wide range of such medical treatment modalities.

It is historically true however that the medical industry has not had apractical methodology for producing high-powered, wavelength specificirradiation in the mid-IR wavelength bands. The present invention wouldallow for such narrow band wavelength specific infrared irradiation andit could do so in a slim, light weight, safe and convenient form factorthat would be easily used for medical applications.

For medical treatment there are some very important advantages to beingable to select the specific wavelength or combination of wavelengthsthat are used for irradiation. Just as in industrial manufacturingmaterials, organic materials also have characteristictransmission/absorption spectral-curves. Animal, plant, or human tissueexhibits specific absorption/transmissive windows which can be exploitedto great advantage.

A very high percentage of the human body is composed elementally ofwater, therefore it is likely that the transmission/absorption curvesfor water are a good starting point for a rough approximation for muchhuman tissue. Through extensive research it is possible to developprecise curves for all types of tissue in humans, animals, and plants.It is also possible to develop the relationship between various kinds ofhealing or stimulation that might be sought from organs or tissue andrelate that to the transmission/absorption curves. By carefullyselecting the wavelength or combination of wavelengths, it would bepossible to develop treatment regimens which could have a positiveeffect with a wide range of maladies and ailments.

Some tissues or organs that it would be desirable to treat are very nearthe surface while others lie deep within the body. Due to the absorptioncharacteristics of human tissue, it might not be possible to reach suchdeep areas with non-invasive techniques. It may be necessary to use someform of invasive technique in order to get the irradiation sources nearthe target tissue. It is possible to design the irradiation arrays ofthe present invention so that they are of the appropriate size and/orshape to be used in a wide range of invasive or non-invasive treatments.While the treatment techniques, modalities and configurations are beyondthe scope of this discussion; the invention is the first of its kindavailable to make solid state, wavelength selective irradiationavailable in the middle-infrared wavelength bands. It can be configuredfor a wide range of modalities and treatment types. Due to its highlyflexible form factor and programmable nature it is capable of beingconfigured for a particular body size and weight to produce theappropriate angles, intensities, and wavelengths for custom treatment.

Infrared radiation is being utilized for an increasing number of medicalapplications from hemorrhoid treatments to dermatology. One example ofinfrared treatment that is currently performed with broadband infraredsources is called infrared coagulation treatment. Additionally, diabeticperipheral neuropathy is sometimes treated with infrared lamptreatments. Tennis elbow and other similar ailments are often currentlytreated with broadband infrared lamps as well. The incorporation of thepresent invention's ability to generate specific wavelengths ofradiation as well as its ability to generate pulsed irradiation mayprovide substantial improvement in these treatments. It also may providefor better patient toleration and comfort. The invention alsofacilitates manufacturing a medical device that could be powered withinherently safe voltages.

The pulsing of the irradiation energy may prove to be a key aspectassociated with many medical treatment applications. Continuousirradiation may cause tissue overheating while a pulsed irradiation mayprove to provide enough stimulation without the deleterious effect ofoverheating, discomfort, or tissue damage. The very fact that thedevices/arrays can be pulsed at extremely high rates with turn-on timesmeasured in microseconds or faster provides another useful property. Itis anticipated that very high intensity pulses of radiation may betolerated without damage to the arrays if they are activated for veryshort duty cycles, since the semi-conductor junction overheat would nothave time to occur with such short pulse times. This would allow greatersummed instantaneous intensity which could facilitate penetrationthrough more tissue.

The frequency at which the pulsing occurs may also prove to beimportant. It is known within the literature that certain frequencies ofirradiation to humans can have healing or, alternatively, deleteriouseffects. For example, certain amplitude modulation frequencies orcombinations of frequencies of visible light can cause humans to becomenauseous and yet other amplitude modulation frequencies or combinationsof frequencies can cause epileptic seizures. As further medical researchis done it may indeed determine that the pulsing frequency, waveformshape, or combination of frequencies along with the selected wavelengthor combination of wavelengths have a very substantial effect on thesuccess of various radiation treatments. It is very likely that many ofthe treatment modalities which will utilize this invention are not yetunderstood nor realized since the subject invention has not beenavailable to researchers or practitioners.

Another application for the subject invention is in the preparationprocessing, or staging of food. Certainly a very wide range of differenttypes of ovens and heating systems have been used in the preparation offood throughout human history. Since most of them are well known, it isbeyond the scope of this patent application to describe the full rangeof such ovens and heating systems. With the notable exception ofmicrowave cooking which utilizes non-infrared/non-thermal source cookingtechnology, virtually all other cooking technologies utilize broadbandheating sources of various types. The infrared heating sources andelements that are used in such ovens are broad-band sources. They do nothave the ability to produce specific wavelengths of infrared energy thatmight be most advantageous to the particular cooking situation or theproduct being cooked.

As was discussed earlier with other materials, plant and animal productshave specific absorption spectral curves. These specific absorptioncurves relate how absorptive or transmissive a particular food productis at specific wavelengths. By selecting a particular wavelength or afew carefully selected wavelengths at which to irradiate the subjectfood it is possible to modify or optimize the desired cookingcharacteristics. The most efficient use of radiated energy can reducethe cost of heating or cooking.

For example, if it is most desirous to heat or brown the outer surfaceof a particular food product, the subject invention would allow for theselection of a wavelength at which that particular food product ishighly absorptive. The result would be that when irradiated at thechosen wavelength the infrared energy would all be absorbed very closeto the surface, thus causing the desired heating and/or browning actionto take place right at the surface. Conversely, if it is desired not tooverheat the surface but rather to cook the food from very deeply withinit, then it is possible to choose a wavelength or combination ofselected wavelengths at which the particular food is much moretransmissive so that the desired cooking result can be achieved. Thusthe radiant energy will be absorbed progressively as it penetrates tothe desired depth.

It is important to note that for electromagnetic waves traveling througha non-metallic material, the intensity of this wave I(t) decreases as afunction of travel distance t as described by the following equation:I(t)=I _(o)(e ^(−αt))In this equation, I_(o) is the initial intensity of the beam and α isthe specific absorption coefficient for the material. As time tincreases, the intensity of the beam undergoes exponential decay whichis caused by radiant energy within the original beam being absorbed bythe host material. For this reason, the use of infrared radiationheating to achieve optimum cooking results entails a complex interactionbetween the thickness of the food items, the applied infrared radiantintensity, the irradiation wavelength, and the material absorptioncoefficient(s).

By mixing RED elements that irradiate at different wavelengths, it ispossible to further optimize a cooking result. Within such amulti-wavelength array, one element type would be chosen at a wavelengthwherein the absorption of radiant energy is low, thus allowing deep-heatpenetration to occur. A second element type would be chosen wherein theabsorption of radiant energy is high thus facilitating surface heatingto occur. Completing the array, a third RED element type could beconceived to be chosen at a wavelength intermediate to these twoextremes in absorption. By controlling the relative radiant output levelof the 3 types of RED emitters contained in such an array, it would bepossible to optimize the important properties of prepared food items.

By connecting color, temperature, and potentially visual sensors to thecontrol system it is possible to close the loop and further optimize thedesired cooking results. Under such circumstances, it may be possible tocheck the exact parameter which might be in question and allow thecontrol system to respond by sending irradiation at the appropriatewavelength, intensity, and direction that would be most desirable. Byutilizing and integrating a vision sensor, it would be possible toactually view the locations and sizes of the food products that are tobe cooked and then optimize the ovens' output accordingly as has beendescribed above. When used in combination with a moisture sensor, itwould be possible to respond with the combination that would maintainthe desired moisture content. It is, therefore, possible to understandhow the subject invention, in combination with the appropriate sensors,and controller “intelligence” can truly facilitate the smart oven of thefuture. It is, of course, possible to combine the present invention withconventional cooking technologies, including convection ovens andmicrowave oven capability to get the best blend of each of thesetechnology offerings. The smart control system could be designed to bestoptimize both the present invention technology in combination with theconventional cooking technologies.

It is also possible, by selecting wavelengths that would be absorbed byone food and not as highly absorbed by a second food, to be veryselective as to the amount of heating that takes place in a mixed plateof food. Thus it can be understood that by changing the combinations andpermutations and intensities of various wavelengths that are selectableone could achieve a wide range of specifically engineered cookingresults.

With any of the applications of the subject invention, it is possible touse various lensing or beam guiding devices to achieve the desireddirectionality of the irradiation energy. This can take the form of arange of different implementations——from individually lensed RED devicesto micro lens arrays mounted proximate to the devices. The chosen beamguiding devices must be chosen appropriately to function at thewavelength of radiation that is being guided or directed. By utilizingwell understood techniques for diffraction, refraction, and reflection,it is possible to direct energy from different portions of an array ofRED devices in desired directions. By programmably controlling theparticular devices that are turned on, and by modulating theirintensities, it is possible to achieve a wide range of irradiationselectivity. By choosing steady state or pulsing mode and by furtherprogramming which devices are pulsed at what time, it is possible toraise the functionality even further.

Though this disclosure discusses the application of radiant energyprimarily within the 1.0 to 3.5 micrometers range, it should be obviousto anyone skilled in the art that similar material heating effects canbe achieved at other operational wavelengths, including longerwavelengths in the infrared or shorter wavelengths down through thevisible region. The spirit of the disclosed invention includes theapplication of direct electron-to-photon solid-state emitters for thepurposes of radiant heating wherein the emitters are conceivablyoperational from the visible through the far infrared. It may bedesirable to, for certain types of applications, to combine otherwavelength selectable devices into the invention which irradiate atother wavelengths outside the mid-infrared range.

FIG. 8 gives a graphical indication of a single RED component 10. TheRED 10 comprises a stack 20. The stack 20 may take a variety ofconfigurations, such as the stacks of semiconductor layers and the likeillustrated in connection with FIGS. 1-7. In at least one form, thecontact 40 (corresponding, for example, to contacts 1105, 1205 and 1305)of the RED 10 is made to the stack 20 through wire 80. When a current 60is made to flow through the bonding wire 80 and the stack 20, photons 70are emitted that possess a characteristic energy or wavelengthconsistent with the configuration of the stack 20.

Because many of the semi-conductor lessons learned in manufacturing LEDsmay apply to REDs, it is useful to mention a parallel that may help theevolution of the new RED devices. Drastic improvements in the energyconversion efficiency (optical energy out/electrical energy in) of LEDshave occurred over the years dating to their introduction into thegeneral marketplace. Energy conversion efficiencies above 10% have beenachieved in commercially available LEDs that operate in the visiblelight and near IR portion of the spectrum. This invention contemplatesthe use of the new REDs operating somewhere within the 1 micrometer to3.5 micrometer range as the primary infrared heating elements withinvarious heating systems. This application describes a specificimplementation in blow molding systems.

FIGS. 9 and 10 show the relative percentage of IR energy transmittedwithin a 10 mil thick section of PET as a function of wavelength. Withinthe quartz transmission range (up to 3.5 micrometer), the presence ofstrong absorption bands (wavelength bands of little or no transmission)are evident at several wavelengths including 2.3 micrometer, 2.8micrometer, and 3.4 micrometer. The basic concept associated with thesubject invention is the use of RED elements designed and chosen tooperate at a selected wavelength(s) within the 1 micrometer to 3.5micrometer range as the fundamental heating elements within the thermalconditioning section of blow molding machines.

FIGS. 11 a, 11 b, and 11 c show an example ensemble of individual REDemitters 10 packaged together into a suitable RED heater element 100. Inthis embodiment of the invention, the REDs 10 are physically mounted sothat N-doped regions are directly attached to a cathode bus 120. Thecathode bus 120 is ideally fabricated out of a material such as copper,or gold, which is both a good conductor of electricity as well as heat.The corresponding regions of the REDs 10 are connected via bond wires 80to the anode bus 110. Ideally, the anode bus would have the same thermaland electrical properties as the cathode bus. Input voltage isexternally generated across the 2 bus bars causing a current (I) to flowwithin the REDs 10 resulting in the emission of IR photons or radiantenergy, such as that shown at 170. A reflector 130 is used in thepreferred embodiment to direct the radiant energy into a preferreddirection away from the RED heater element 100. The small physicalextent of the REDs 10 make it possible to more easily direct the radiantenergy 170 that is emitted into a preferred direction. This statementbeing comparatively applied to the case of a much larger coiledfilament; such a relationship between the physical size of an emitterand the ability to direct the resultant radiant flux using traditionallensing means being well known in the art.

A heat sink 140 is used to conduct waste heat generated in the processof creating IR radiant energy 170 away from the RED heater element 100.The heat sink 140 could be implemented using various means known withinindustry. These means include passive heat sinking, active heat sinkingusing convection air cooling, and active heat sinking using water orliquid cooling. The liquid cooling through, for example, a liquid jackethas the advantage of being able to conduct away the substantial amountof heat that is generated from the quantity of electrical energy thatwas not converted to radiant photons. Through the liquid media, thisheat can be conducted to an outdoor location or to another area whereheat is needed. If the heat is conducted out of the factory or toanother location then air conditioning/cooling energy could besubstantially reduced.

Additionally, a bulb 150 is optimally used in this embodiment of theinvention. The primary function of the bulb 150 as applied here is toprotect the REDs 10 and bonding wires 80 from being damaged. The bulb150 is preferably constructed out of quartz due to its transmissionrange that extends from the visible through 3.5 micrometer. However,other optical materials including glass having a transmission rangeextending beyond the wavelength of operation of the REDs 10 could alsobe used.

One deployment of the RED heater element 100, within a blow molder, isdepicted in FIGS. 12 a and 12 b. In this system, preforms 240 enter intoa thermal monitoring and conditioning system 210 via a transfer system220. The preforms 240 could come into the thermal monitoring and controlsystem 210 at room temperature, having been previously injection moldedat some earlier time. Or, alternatively, the preforms 240 could comedirectly from an injection molding process as is done in single-stageinjection molding/blow molding systems. Alternatively, the preformscould be made by one of several other processes. Whatever the form andtiming of preform manufacturing, entering in this fashion, the preforms240 would have varying amounts of latent heat contained within them.

Once presented by the transfer system 220, the preforms 240 aretransported through the thermal monitoring and control system 210 via aconveyor 250, such conveyors being well known in industry. As thepreforms 240 travel through the thermal monitoring and control system210, they are subjected to radiant IR energy 170 emitted by a series ofRED heater elements 100. The IR energy 170 emitted by these RED heaterelements 100 is directly absorbed by the preforms 240 in preparation ofentering the blowing system 230. It should be appreciated that theenergy may be continuous or pulsed, as a function of the supply or drivecurrent and/or other design objectives. The control system, such controlsystem 280, in one form, controls this functionality. As an option, thecontrol system is operative to pulse the system at electrical currentlevels that are substantially greater than recommended steady statecurrent levels to achieve higher momentary emitted intensity in pulsedoperation and respond to an input signal from an associated sensorcapability to determine a timing of the pulsed operation

In the preferred embodiment of a blow molder operating using the methodand means described by this invention, a convection cooling system 260is also preferably deployed. This system removes waste heat from the airand mechanics that are in proximity to the preforms 240 under process. Aconduction cooling device may also be employed to do so. Heating ofpreforms by convection and/or conduction is known in the art to bedeleterious to the overall thermal conditioning process. This is becausePET is a very poor thermal conductor and heating the outer periphery ofthe preform results in uneven through heating, with too cool a centerand a too warm outer skin.

Also contained within the preferred system embodiment are temperaturesensors 270 (which may take the form of an intelligent sensor or camerathat is capable of monitoring a target in at least one aspect beyondthat which a single point temperature measurement sensor is capable) anda temperature control system 280. These aspects of the preferred blowmolder design are particularly applicable to the attributes of aone-stage blow molding system. In a one-stage blow molding system, thepreforms 240 enter into the thermal monitoring and conditioning system210 containing latent heat energy obtained during the injection moldingstage. By monitoring the temperature and thus the heat content of theincoming preforms 240 (or specific subsections of such performs), it ispossible for a temperature monitoring and control system 280 to generatepreform-specific (or subsection specific) heating requirements and thencommunicate these requirements in the form of drive signals to theindividual RED heater elements 100. The solid-state nature andassociated fast response times of RED emitters 10 make them particularlysuited to allow the electrical supply current or on-time to be modulatedas a function of time or preform movement. Also, subsections of the REDarray may be controlled, as will be appreciated.

The temperature control system 280 used to enact such output controlcould be implemented as an industrial PC as custom embedded logic or asor an industrial programmable logic controller (PLC), the nature andoperation all three are well known within industry. The control system,such as that shown as 280, may be configured a variety of ways to meetthe objectives herein. However, as some examples, the system may controlon/off status, electrical current flow and locations of activateddevices for each wavelength in an RED array.

FIGS. 13-16 illustrate methods according to the present invention. Itshould be appreciated that these methods may be implemented usingsuitable software and hardware combinations and techniques. For example,the noted hardware elements may be controlled by a software routinesstored and executed with the temperature control system 280.

Referring now to FIG. 13, a preferred method 300 for the thermaltreatment of thermoplastic preforms is shown outlining the basic stepsof operation. Preforms 240 are transported via a conveyor 250 through athermal monitoring and control system 210 (Step 305). Of course, itshould be understood that, with all embodiments showing conveyance, asimple means to locate the articles for exposure, with or withoutconveyance, may be employed. The preforms 240 are irradiated using REDheater elements 100 contained within the thermal monitoring and controlsystem 210 (Step 310). A convection cooling system 260 is used to removewaste heat from the air and mechanical components within the thermalmonitoring and control system 210 (Step 315).

Another method 301 for the treatment of thermoplastic preforms isoutlined in FIG. 14. In method 301, (Step 310), the process ofirradiating preforms 240 using RED heater elements 100, is replaced withStep 320. During Step 320 of method 301, preforms 240 are pulseirradiated synchronously to their motion through the thermal monitoringand conditioning system 210. This synchronous, pulse irradiationprovides substantial additional energy efficiency because the REDdevices nearest the perform are the only ones that are turned on at anygiven instant. In one form, the maximum output of the pulsed energy issynchronously timed to the transport of individual targets.

Yet another method 302 for the treatment of thermoplastic preforms isoutlined in FIG. 15. In this method 302, the temperature of incomingpreforms 240 is measured using temperature sensors 270. This is done togauge the latent heat energy of preforms 240 as they enter into thesystem (Step 325). The preforms 240 are then transported via a conveyor250 through a thermal monitoring and control system 210 (Step 305). Atemperature control system 280 using the temperature informationsupplied by the temperature sensors 270 to generate a preferred controlsignal to be applied to the RED heater elements 100 (Step 330). Thepreferred control signal is then communicated from the temperaturecontrol system 280 to the RED heater elements 100 (Step 335). Thepreforms 240 are then irradiated using the RED heater elements 100contained within the thermal monitoring and control systems 210 (Step310). A convection cooling system 260 is then used to remove waste heatfrom the air and mechanical components within the thermal monitoring andcontrol system 210 (Step 315).

Still another method 303 of the treatment of thermoplastic preforms isoutlined in FIG. 16. In method 303, Step 310, the process of irradiatingpreforms 240 using RED heating elements 100, is replaced with Step 320.During Step 320 of method 303, preforms 240 are pulse irradiatedsynchronously to their motion through the thermal monitoring andconditioning system 210.

The above description merely provides a disclosure of particularembodiments of the invention and is not intended for the purpose oflimiting the same hereto. As such, the invention is not limited to onlythe above-described applications or embodiments. This disclosureaddressed many applications of the invention broadly and one applicationembodiment specifically. It is recognized that one skilled in the artcould conceive of alternative applications and specific embodiments thatfall within the scope of the invention.

1. A system for non-contact thermal treatment of plastic targetcomponents prior to molding or processing operations comprising: a meansoperative to locate plastic target components in a manner facilitatingthe application of radiant heating; and a thermal monitoring and controlsection into which the plastic components are located for exposure, thethermal monitoring and control section comprising one or more solidstate RED-based radiant heating elements operative to emit radiantenergy in a narrow wavelength band matching a desired absorptivecharacteristic of the plastic target components via a direct electricalcurrent-to-photon conversion process.
 2. The system as set forth inclaim 1 wherein the means operative to locate is a conveyance meansoperative to transport the plastic target components.
 3. The system asset forth in claim 1 wherein an electrical supply current is continuousto the RED-based radiant heating elements whereby a continuous radiantenergy output results.
 4. The system as set forth in claim 1 wherein theRED-based radiant heating elements are operative to emit radiant energyin a pulsed mode, with the time of maximum output synchronously-timed tothe transport of individual molded target component through the thermalmonitoring and control section.
 5. The system as set forth in claim 1further comprising at least one of a convection cooling device or aconduction cooling device configured to remove waste heat from air andmechanical components within the thermal monitoring and control section.6. The system as set forth in claim 1 further comprising a temperaturesensor configured to measure temperature of individual target componentsprior to entering the thermal monitoring and control section wherebylatent heat content can be determined.
 7. The system as set forth inclaim 6 wherein a temperature control system is used to generate controlsignals to apply to the RED-based radiant heating elements based on atarget component temperature.
 8. The system as set forth in claim 7wherein the temperature of subsections of the target component aremeasured and is used to generate control signals to apply RED-basedradiant heating to subsections of a target component.
 9. The system asset forth in claim 1 wherein the RED-based radiant heating elements areoperative to emit radiant energy within a range of 1 to 3.5 micrometerwavelength.
 10. The system as set forth in claim 1 wherein the RED-basedradiant heating elements are operative to emit radiant energy within atleast one narrow wavelength range specifically tuned to the heatingrequirements of a particular target component application.
 11. A methodof thermally treating thermoplastic preforms prior to stretch blowmolding operations, the method comprising the steps of: transporting aseries of preforms through a thermal monitoring and control section of ablow molding machine; irradiating the preforms using RED-based radiantheating elements operative to emit radiant energy in a narrow wavelengthband matching a desired absorptive characteristic of the preforms; andremoving waste heat from air and mechanical components of the thermalmonitoring and control section of the blow molding machine using acooling system.
 12. The method as set forth in claim 11 wherein theRED-based radiant heating elements are operated in a pulsed modesynchronous to the transport of individual preforms.
 13. The method asset forth in claim 11 further comprising the steps of: measuringtemperature of incoming preforms to gauge latent heat content prior toentering the thermal monitoring and control section; generating controlsignals to apply to the RED-based radiant heating elements based on theincoming preform temperatures; and communicating these control signalsto the RED-based radiant heating elements.
 14. The method as set forthin claim 11 further comprising measuring the temperature of subsectionsof a target component and generating control signals to apply RED-basedradiant heating to the subsections.
 15. The method as set forth in claim13 wherein the RED-based radiant heating elements are operated in apulsed mode synchronous to the transport of individual preforms.
 16. Asystem for selectively injecting radiant heat into a target, the systemcomprising: at least one solid state radiation emitting device element(RED), the at least one RED element being operative to emit radiation ina narrow wavelength band of radiant heat output to match desiredabsorptive characteristics of the target; a mounting arrangement toposition the at least one RED element such that irradiation therefrom isdirected at the target; and a means for supplying electrical current tothe at least one RED element whereby a direct electricalcurrent-to-photon radiation conversion process occurs.
 17. The system asset forth in claim 10 wherein the at least one RED element takes theform of an x by y array of individual RED devices.
 18. The system ofclaim 16 wherein the at least one RED element takes the form of acustomized arrangement of individual RED devices.
 19. The system ofclaim 17 wherein the arrays are in the form of chip-on-board x by yarrays of individual RED devices mounted directly in a chip-on-boardconfiguration.
 20. The system of claim 17 wherein the circuit boards onwhich the RED devices are mounted on circuit boards chosen to beoperative to conduct heat away from the RED devices.
 21. The system ofclaim 20 wherein the circuit boards on which the RED devices are mountedhave heat sink devices associated therewith for conducting heat awayfrom the RED devices and the circuit board.
 22. The system of claim 20wherein means for conducting heat away includes a liquid heat exchangejacket operative to move the heat a substantial distance from thesystem.
 23. The system of claim 17 wherein the x by y array ofindividual RED devices comprises at least some RED devices operative toproduce more than one selected narrow wavelength band of infraredradiation in a range from 1 micrometer to 5 micrometer.
 24. The systemof claim 17 wherein the x by y array comprises a mix of RED deviceswhich represents at least two different selected narrow wavelength bandsof infrared radiation in a range from 1 micrometer to 5 micrometer. 25.The system of claim 17 further comprising a control system configured toseparately control at least one of on/off status, electrical currentflow, and locations of activated devices for each wavelength representedin the array.
 26. The system of claim 17 further comprising a controlsystem configured to have separate control of sub-sections of the arrayfor at least one of position within the array and intensity of output.27. The system of claim 16 further comprising a control systemconfigured to supply the electrical drive current to facilitate a pulsedmode of operation.
 28. The system of claim 27 wherein the control systemis operative to pulse the system at electrical current levels that aresubstantially greater than recommended steady state current levels toachieve higher momentary emitted intensity in pulsed operation andrespond to an input signal from an associated sensor capability todetermine a timing of the pulsed operation.
 29. The system of claim 28wherein the control system further comprises the ability to synchronizethe pulsing operation with moving targets.
 30. The system of claim 16wherein the at least one RED element comprises an array of multiple REDdevices configured in an arrangement in a substantially non-planarconfiguration.
 31. The system of claim 30 wherein the RED devices aredeployed on multiple circuit boards configured in a three dimensionalarrangement whereby better irradiation of a certain type of targetresults.
 32. The system of claim 24 wherein the array further comprisesRED devices operative to produce wavelengths in a range outside the 1 to5 micrometers range.
 33. The system of claim 16 wherein the means forproviding electrical current is a programmable control system operativeto control at least one aspect of system irradiation output.
 34. Thesystem of claim 33 wherein the programmable control system comprises atleast one input from a temperature sensor and is operative to change atleast one output parameter in accordance with the at least onetemperature sensor input.
 35. The system of claim 34 wherein theprogrammable control system further comprises an intelligent sensorinput to monitor other parameters about the target to provide data usedin modification of at least one aspect of the system irradiation output.36. The system of claim 35 wherein the intelligent sensor comprises acamera system.
 37. The system of claim 34 wherein the temperature sensorcomprises a thermal infrared camera operative to monitor the target inat least one aspect beyond that which can be monitored by a single pointtemperature measurement sensor.
 38. The system of claim 1 wherein theplastic target components comprise at least one of PET preforms or PETbottles.
 39. A heat injection method applied to a target, the methodcomprising: locating the target for exposure to at least one radiationemitting device; selectively supplying electrical current to the atleast one radiation emitting device; and, selectively injecting heat inat least one selected narrow wavelength band into the target by theradiation emitting device based on the selected supplied electricalcurrent, the selected narrow wavelength band matching desired absorptivecharacteristics of the target.
 40. The method as set forth in claim 39wherein the at least one radiation emitting device is operational in apulse mode.
 41. The method as set forth in claim 39 further comprisingmeasuring a temperature of the target and controlling the selectivesupplying of electrical current based on the temperature.
 42. The systemas set forth in claim 1 wherein the radiant heat is partially or fullyabsorbed by the plastic target components.
 43. The system as set forthin claim 1 wherein the wavelength band corresponds to a strongabsorption band for the plastic target components.
 44. The system as setforth in claim 43 wherein the strong absorption band is at approximately1.65 micrometers.
 45. The system as set forth in claim 43 wherein thestrong absorption band is at approximately 2.3 micrometers.
 46. Thesystem as set forth in claim 1 wherein the narrow wavelength band isbetween 1.6 micrometers to 2.5 micrometers.
 47. The system as set forthin claim 1 wherein the narrow wavelength band is between 1.6 micrometersto 3.0 micrometers.
 48. The system as set forth in claim 1 wherein thenarrow wavelength band is between 1.55 micrometers to 2.0 micrometers.49. A system for non-contact thermal treatment of plastic targetcomponents prior to molding or processing operations comprising: a meansoperative to locate plastic target components in a manner facilitatingthe application of radiant heating; and a thermal monitoring and controlsection into which the plastic components are located for exposure, thethermal monitoring and control section comprising one or moresemiconductor-based narrow wavelength band radiant heating elementsoperative to emit radiant energy in a narrow wavelength band matching adesired absorptive characteristic of the plastic target components via adirect electrical current-to-photon conversion process.
 50. The systemof claim 49 wherein the plastic target components comprise at least oneof PET performs or PET bottles.
 51. A method of thermally treatingthermoplastic preforms prior to stretch blow molding operations, themethod comprising the steps of: transporting a series of preformsthrough a thermal monitoring and control section of a blow moldingmachine; irradiating the preforms using narrow wavelength band radiantheating elements operative to emit radiant energy in a narrow wavelengthband matching a desired absorptive characteristic of the preforms; andremoving waste heat from air and mechanical components of the thermalmonitoring and control section of the blow molding machine using acooling system.
 52. The method of claim 51 wherein the thermoplasticperforms are PET preforms.
 53. A system for selectively injectingradiant heat into a target, the system comprising: at least one narrowwavelength band emitting element, the at least one narrow wavelengthband element being operative to emit radiation in a narrow wavelengthband of radiant heat output to match desired absorptive characteristicsof the target; a mounting arrangement to position the at least onenarrow wavelength band element such that irradiation therefrom isdirected at the target; and a means for supplting electrical current tothe at least one narrow wavelength band element whereby a directelectrical current-to-photon radiation conversion process occurs.